Quantum dot light-emitting diode and display apparatus thereof

ABSTRACT

A quantum dot light-emitting diode and a display apparatus comprising the quantum dot light-emitting diode are provided. The quantum dot light-emitting diode comprises an anode, a hole injecting layer, a hole transporting layer, a quantum dot light-emitting layer, an electron transporting layer and a cathode from bottom to top, wherein the materials of the quantum dot light-emitting layer contain quantum dots and CuSCN nano-particles. By blending quantum dots and CuSCN nano-particles into a membrane to prepare a quantum dot light-emitting layer, a hole trap state on the surface of the quantum dots is passivated, and the transporting effect of a hole is improved, so that the injection of holes in the quantum dot light-emitting diode and that of electrons achieve balance, and thus the light-emitting efficiency and stability are improved.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a national stage application of PCT PatentApplication No. PCT/CN2017/099061, filed on 25 Aug. 2017, which claimspriority to Chinese Patent Application No. 2016/11,015,977.6, filed on18 Nov. 2016, the content of all of which is incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to the field of quantum dot(QD)light-emitting diode technology, and more particularly, to a QDlight-emitting diode and a preparation method therefor, and alight-emitting module and a display apparatus.

BACKGROUND

A QD light-emitting diode (QLED) based on a fluorescent semiconductorhas a plurality of advantages including a high color purity, a goodstability, a long life, a good color temperature, and a simplepreparation process, which has a huge application prospect in a flatpanel displayer and a solid-state lighting of a next generation

A performance of a QD material and a QLED device has been improvedrapidly, through a continuous effort of a plurality of researchers.However, the QLED in the present art still has a plurality of problemsto be solved, including a light-emitting efficiency is still far awayfrom an industrial production, an exploration for a large-scalepreparation process and more. Wherein in the QLED devices, an injectionimbalance of a carrier (an electron and a hole) is a key factoraffecting the light-emitting efficiency of the QLED devices and alifetime of the devices. For example, a valence band of a core-shell QDwidely used and based on a CdSe@ZnS (Cadmium selenide @Zinc Sulfide) isgenerally higher than 6 eV, while a HOMO energy level of most organicholes transport layers is lower than 6 eV, thus there is a limitationexisting when the hole is transported from the organic holes transportlayer to a QD light-emitting layer, whereas a QD conduction band isgenerally higher than 4 eV, and an electron is easily injected from anelectron transport layer into the QD light-emitting layer. A difficultyof the injection of holes is different to that of the electrons,resulting in a number of the holes and a number of the electronsimbalance in the QD light-emitting layer, while excess electronsaccumulate in the QD light-emitting layer, causing the QDs to carry acharge, thus a plurality of excitons are easy to generate an augerrecombination, causing the luminescence to annihilate, greatly affectingthe light-emitting efficiency of the device. In addition, there are alarge plurality of hole trap states on a surface of the QD, shown asFIG. 1, wherein, 10 is a holes transport layer, 11 is a QD, 12 is anelectrons transport layer, and the QDs are also easily agglomerated, andgenerating a concentration quenching. All of these are seriouslyaffecting a performance of the QLED devices.

In order to solve a problem mentioned above of the injection imbalancebetween the holes and the electrons in the QLED devices, a plurality ofsearchers have tried various methods, including introducing anultra-thin insulating material between the electrons transport layer andthe QD light-emitting layer to slow down an injection rate of theelectrons, however the QLED devices obtained by this method have acomplicated structure, a cumbersome process, and it is hard to control athickness of an insulating layer, not conducive to a mass production. Inaddition, some researchers have blended the QDs with a plurality ofconductive polymers including polyvinylcarbazole (PVK), blocking theinjection of the electrons but improving the injection of the holes byusing an energy level characteristic of the PVK, however a compatibilitybetween an organic polymer and an inorganic QD is poor, causing a poorfilm formation effect, resulting in an uneven distribution of the QDs ina mixture layer of the organic polymer-QD, and the exciton is also easyto have an Auger recombination, affecting a performance of the device.In addition, it has also been reported that, a doped or undopedinorganic holes transport material such as NiO (Nickel oxide), CuO(cupric oxide), MoO₃ (molybdenum trioxide) or the like has been used asa holes transport layer, to substitute a conventional organic holestransport material, although it is possible to improve the injectioneffect of the holes to some extent, a problem of the carrier injectionimbalance in the QLED devices is still unable to overcome.

Therefore, the current technology needs to be improved and developed.

BRIEF SUMMARY OF THE DISCLOSURE

According to the defects described above in the prior art, the purposeof the present disclosure is providing a QD light-emitting diode and apreparation method therefor, and a light-emitting module and a displayapparatus, in order to solve the problems in the prior art that thecarrier injection imbalance in the QLED devices.

In order to solve the technical problems mentioned above, the technicalsolution of the present disclosure is as follows:

A QD light-emitting diode, wherein the QD light-emitting diode comprisesan anode, a cathode, and a QD light emitting layer arranged between theanode and the cathode;

wherein a material of the QD light-emitting layer comprises a pluralityof QDs and a plurality of CuSCN (Copper thiocyanate) nanoparticles.

The QD light-emitting diode further comprises a holes injection layerarranged between the anode and the QD light emitting layer, a holestransport layer arranged between the holes injection layer and the QDlight emitting layer, and an electrons transport layer arranged betweenthe cathode and the QD light-emitting layer, the holes transport layeroverlays the QD light-emitting layer.

The QD light-emitting diode, wherein a mass ratio between the QDs andthe CuSCN nanoparticles is 0.001˜20:1.

The QD light-emitting diode, wherein a thickness of the QDlight-emitting layer is 10˜100 nm.

The QD light-emitting diode, wherein a size range of the CuSCNnanoparticles is 0.5˜50 nm.

A preparation method of the QD light-emitting diode described in any oneabove, wherein comprising:

prepare a QD light-emitting layer on the anode; wherein the QDlight-emitting layer is prepared by the QDs and the CuSCN nanoparticles;

prepare a cathode on the QD light-emitting layer, and form the QDlight-emitting diode.

The preparation method of the QD light-emitting diode, wherein the stepof preparing the QD light-emitting layer on the anode includesspecifically: depositing a mixture of the QDs and the CuSCNnanoparticles on the anode by a solution method, to form a QDlight-emitting layer containing the CuSCN nanoparticles.

The preparation method of the QD light-emitting diode, wherein the stepof preparing the QD light-emitting layer on the anode includesspecifically: blending the QDs and the CuSCN nanoparticles, beforedepositing on the anode through an evaporation method, and forming a QDlight-emitting layer containing the CuSCN nanoparticles.

The preparation method of the QD light-emitting diode, wherein furthercomprising:

step A, prepare a holes injection layer on the anode;

step B, then prepare a holes transport layer on the holes injectionlayer;

step C, followed by preparing a QD light-emitting layer on the holestransport layer; wherein the QD light-emitting layer is prepared from amixture of the QDs and the CuSCN nanoparticles;

step D: finally, prepare an electrons transport layer on the QDlight-emitting layer, and vapor deposit a cathode on the electronstransport layer before forming a QD light-emitting diode.

The preparation method of the QD light-emitting diode, wherein the stepC includes specifically: spin-coat a mixture of the QDs and the CuSCNnanoparticles on the holes transport layer to form a QD light-emittinglayer containing the CuSCN nanoparticles.

The preparation method of the QD light-emitting diode, wherein in themixture, a concentration of the QDs is 1˜50 mg/mL, and a concentrationof the CuSCN nanoparticles is 0.001˜50 mg/m L.

The preparation method of the QD light-emitting diode, wherein in themixture, the concentration of the QDs is 10˜20 mg/mL, and theconcentration of the CuSCN nanoparticles is 0.01˜10 mg/mL.

The preparation method of the QD light-emitting diode, wherein a massratio between the QDs and the CuSCN nanoparticles is 0.001˜20:1.

A light-emitting module, wherein comprising the QD light-emitting diodedescribed above.

A display apparatus, wherein comprising the light-emitting moduledescribed above.

Benefits: the present disclosure blends the QDs and the CuSCNnanoparticles into a membrane to prepare the QD light-emitting layer,and passivates a hole trap state on a surface of the QDs, as well asimproving a transport effect of the holes, making an injection of theholes and the electrons in the QLED achieve a balance, thus improving alight-emitting efficiency and a stability of the QLED.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a diagram on a transport mechanism of a carrier inthe QD light-emitting layer in a conventional QD light-emitting diode.

FIG. 2 illustrates a schematic diagram on a preferred embodiment of theQD light-emitting diode disclosed in the present disclosure.

FIG. 3 illustrates a diagram on a transport mechanism of a carrier inthe QD light-emitting layer of the QD light-emitting diode disclosed inthe present disclosure.

FIG. 4 illustrates a flow chart on a preferred embodiment of thepreparation method of the QD light-emitting diode disclosed in thepresent disclosure.

FIG. 5 illustrates a schematic diagram on an energy level of the QDlight-emitting diode in the example 1 of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

The present disclosure provides a QD light-emitting diode and apreparation method therefor, and a light-emitting module and a displayapparatus, in order to make the purpose, technical solution and theadvantages of the present disclosure clearer and more explicit, furtherdetailed descriptions of the present disclosure are stated here,referencing to the attached drawings and some preferred embodiments ofthe present disclosure. It should be understood that the detailedembodiments of the disclosure described here are used to explain thepresent disclosure only, instead of limiting the present disclosure.

Referencing to FIG. 2, which illustrates a schematic diagram on apreferred embodiment of the QD light-emitting diode disclosed in thepresent embodiment, shown as the figure, the QD light-emitting diodecomprises sequentially from bottom up, an anode 1, a holes injectionlayer 2, a holes transport layer 3, a QD light-emitting layer 4, anelectron transport layer 5 and a cathode 6; wherein a material of the QDlight-emitting layer 4 comprises a plurality of QDs 41 and a pluralityof CuSCN nanoparticles 42.

The present embodiment forms a membrane from a mixture containing aplurality of QDs and a plurality of CuSCN nanoparticles, to prepare a QDlight-emitting layer, because the CuSCN nanoparticles used has not onlyan excellent holes transport ability, but also a rich source and a lowercost. In addition, as shown in FIG. 3, wherein 20 is a holes transportlayer, 21 is a plurality of CuSCN nanoparticles, 22 is a plurality ofQDs, and 23 is an electrons transport layer, through blending the CuSCNnanoparticles 21 and the QDs 22, and forming a membrane, a plurality oftiny CuSCN nanoparticles 21 are filling in a plurality of gaps betweenthe QDs 22, acting as an additive for a holes transport, which on onehand, is able to passivate a hole trap state on a surface of the QDs 22,and on the other hand, is acting as a bridge for the holes transport inthe QD light-emitting layer, improving a holes transport effect, andovercomes effectively a plurality of problems including a carrier (ahole and an electron) injection imbalance causing a device performancedegradation in a QLED device.

The present embodiment dissolves the QDs and the CuSCN nanoparticles ina solvent, and forms a mixture, before depositing the mixture andforming a QD light-emitting layer containing a plurality of CuSCNnanoparticles. Wherein a mass ratio between the QDs and the CuSCNnanoparticles is 0.001˜20:1.

Preferably, a thickness of the QD light-emitting layer described in thepresent embodiment is 10˜100 nm, for example, the thickness may be 50nm, 80 nm or 100 nm.

Preferably, a size range of the CuSCN nanoparticles described in thepresent embodiment is 0.5˜50 nm, for example, the size range may be 5nm, 10 nm or 30 nm.

The CuSCN nanoparticles described in the present embodiment may be adoped or undoped CuSCN material. The CuSCN nanoparticles may be preparedby a chemical method or a physical method, wherein the chemical methodincludes but not limited to, a sol-gel method, a chemical bathdeposition method, a chemical vapor deposition method, a hydrothermalmethod, a co-precipitation method, and an electrochemical depositionmethod; the physical method includes but not limited to, a thermalevaporation coating method, an electron beam evaporation coating method,a magnetron sputtering method, a multi-arc ion plating method, and anelectrolysis method.

The CuSCN nanoparticles embedding in the gaps between the QDs, on onehand, it is able to passivate the hole trap state on the surface of theQDs, and on the other hand, it is able to reduce an energy barrier ofthe holes injecting into the QDs, improving a transport efficiency ofthe holes, making an injection number in the QD light-emitting layerbetween the holes and the electrons get balanced, thus improving alight-emitting efficiency of the QLED device.

Specifically, the QDs of the present embodiment may be, but not limitedto, one or more of an II-V compound semiconductor, an III-V compoundsemiconductor, an IV-VI compound semiconductor and a core-shellstructure thereof.

Specifically, the anode of the present embodiment may be, but notlimited to, one or more of indium doped tin oxide (ITO), fluorine dopedtin oxide (FTO), antimony doped tin oxide (ATO), and aluminum doped zincoxide (AZO).

Specifically, the holes injection layer may be, but not limited to, oneor more of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid(PEDOT:PSS), CuPc (Copper(II) phthalocyanine), F4-TCNQ(2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane), HATCN(dipyrazino[2,34:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile),undoped transition metal oxide, doped transition metal oxide, metalsulfur group compound, doped metal sulfur group compound. Wherein, thetransition metal oxide may be, but not limited to, MoO₃, VO₂, WO₃, CrO₃,CuO or a mixture thereof; the metal sulfur group compound may be, butnot limited to, MoS₂, MoSe₂, WS₂, WSe₂, CuS or a mixture thereof.

Specifically, the holes transport layer in the present embodiment may beselected from an organic material having a holes transport ability, andmay be, but not limited to,poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB),polyvinyl carbazole (PVK),poly(N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine) (poly-TPD),poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine) (PFB),4,4′,4″-tris(carbazol-9-yl)-triphenylamine (TCTA),4,4′-bis(carbazol-9-yl)biphenyl (CBP),N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)-1,1′-biphenyl-4,4′-diamine(TPD),N,N′-bis-(1-naphthalenyl)-N,N′-bis(phenyl)-1,1′-biphenyl-4,4′-diamine(NPB),doped graphene, undoped graphene, C60 or a mixture thereof.

Specifically, the holes transport layer in the present embodiment mayfurther be selected from an inorganic material having the holestransport ability, and may be, but not limited to, NiO, WO₃, MoO₃, CuO,VO₂, CrO₃, MoS₂, MoSe₂, WS₂, WSe₂, CuS, or a mixture thereof.

Specifically, a material of the electrons transport layer in the presentembodiment may be one or more of n-type ZnO, TiO₂, SnO₂, Ta₂O₃, AlZnO,ZnSnO, InSnO, Alq₃, Ca, Ba, CsF, LiF, CsCO₃. Preferably, the electronstransport layer is n-type ZnO, an n-type TiO₂.

Specifically, a material of the cathode in the present embodiment maybe, but not limited to, one or more of Al, Ag, Cu, Mo, Au, or an alloythereof.

The QD light-emitting diode of the positive structures described abovein the present embodiment is not limited to the functional layersdescribed above, and may further include an interface functional layeror an interface modification layer, which includes but not limited to,one or more of an electron blocking layer, a hole blocking layer, anelectrode modification layer and an isolation protection layer.

It should be noted that the mixture of the QDs and the CuSCNnanoparticles in the present embodiment is not limited to preparing a QDlight-emitting diode having a positive structure, but also being able toprepare a QD light-emitting diode having an inverted structure. The QDlight-emitting diode having the inverted structure is not limited to thefunctional layers described above, and may further include an interfacefunctional layer or an interface modification layer, which comprises,but not limited to, one or more of the an electron blocking layer, ahole blocking layer, an electrode modification layer, and an isolateprotection layer.

The present embodiment further provides a light-emitting module, whichcomprises the QD light-emitting diode described above.

The present embodiment further provides a display apparatus, whichcomprises the QD light-emitting diode described above, or thelight-emitting module described above.

Based on the QD light-emitting diode, the present embodiment furtherprovides a flow chart on a preferred embodiment of a preparation methodof the QD light-emitting diode disclosed in the present embodiment,shown as FIG. 4, comprising:

step S100, prepare a holes injection layer on the anode;

step S200, then prepare a holes transport layer on the holes injectionlayer;

step S300, followed by preparing a QD light-emitting layer on the holestransport layer; wherein the QD light-emitting layer is prepared from amixture of the QDs and the CuSCN nanoparticles;

step S400: finally prepare an electrons transport layer on the QDlight-emitting layer, and vapor deposit a cathode on the electronstransport layer before forming a QD light-emitting diode.

Specifically, the step S300 of the present embodiment comprises:spin-coat a mixture of the QDs and the CuSCN nanoparticles on the holestransport layer to form a QD light-emitting layer containing the CuSCNnanoparticles.

The present embodiment blends the QDs with the CuSCN nanoparticles,before forming a CuSCN-enhanced QD light-emitting layer by anevaporation method or a solution film formation method including aplurality of processes of a spin coating, an ink spraying, a bladecoating or the like.

The present embodiment dissolves the QDs and the CuSCN nanoparticles ina solvent to form a mixture, before depositing the mixture and forming aQD light-emitting layer containing the CuSCN nanoparticles. Wherein, amass ratio of the QDs to the CuSCN nanoparticles is 0.001˜20:1. In themixture, a concentration of the QDs is 1 to 50 mg/mL, a concentration ofthe CuSCN nanoparticles is 0.001 to 50 mg/mL. Preferably, in themixture, a concentration of the QDs is 10-20 mg/mL, and a concentrationof the CuSCN nanoparticles is 0.01-10 mg/mL. A solvent used in themixture may be, but not limited to, one or more of an n-octane, anisooctane, a toluene, a benzene, a chlorobenzene, a xylene, achloroform, an acetone, a cyclohexane, an n-hexane, an n-pentane, anisopentane, an n-butyl ether, an anisole, a phenethyl ether, anacetophenone, an aniline, a diphenyl ether, an N,N-dimethylformamide, anN-methylpyrrolidone, a dimethyl sulfoxide, a hexamethylphosphoramide.

The preparation method of the functional layers described above of thepresent embodiment may be a chemical method or a physical method,wherein the physical method includes, but not limited to, a spin coatingmethod, a spray coating method, a roll coating method, a typing method,a printing method, an inkjet method, a dip coating method, a thermalevaporation coating method, an electron beam evaporation coating method,a magnetron sputtering method, a multi-arc ion plating method; thechemical methods include, but not limited to, a chemical vapordeposition method, a successive ionic layer adsorption and reactionmethod, an anodization method, an electrolytic deposition method, acoprecipitation method.

The preparation method disclosed in the present embodiment is simple,and may solve effectively a plurality of problems in the prior art of apoor film formation, a complicated structure, a high material cost and adifficult industrialization. In addition, the prepared device has anexcellent performance, a good stability, and a long service life.

A detailed description is listed herein, taking a preparation process ofthe QD light-emitting layer and a preparation process of the QLED deviceas examples.

EXAMPLE 1

1) Prepare a mixture of the CuSCN nanoparticles and the QDs: dissolve 10mg CuSCN powder and 15 mg CdSe@ZnS QDs in 1 mL n-octane, mix well andform a uniform mixture.

2). A plurality of preparation steps of the QLED device is as follows:spin coat a layer of the PEDOT:PSS holes injection layer on the ITOsubstrate; spin coat a layer of the PVK holes transport layer on thePEDOT:PSS holes injection layer;

3). Spin-coat the mixture of the CuSCN nanoparticles and the QDs on thePVK holes transport layer, and form a QD light-emitting layer containingthe CuSCN nanoparticles;

4). Followed by spin-coating a layer of the ZnO electrons transportlayer on the QD light-emitting layer;

5). Finally, an Al cathode is evaporated on the ZnO electrons transportlayer, to obtain the QD light-emitting diode, whose energy levelstructure is shown in FIG. 5.

EXAMPLE 2

1) Prepare a mixture of the CuSCN nanoparticles and the QDs: dissolve 5mg CuSCN powder and 15 mg CdSe@ZnS QDs in 1 mL n-octane, mix well andform a uniform mixture.

2). A plurality of preparation steps of the QLED device is as follows:spin coat a layer of the PEDOT:PSS holes injection layer on the ITOsubstrate;

spin coat a layer of the PVK holes transport layer on the PEDOT:PSSholes injection layer;

3). Spin-coat the mixture of the CuSCN nanoparticles and the QDs on thePVK holes transport layer, and form a QD light-emitting layer containingthe CuSCN nanoparticles;

4). Followed by spin-coating a layer of the ZnO electrons transportlayer on the QD light-emitting layer;

5). Finally, an Al cathode is evaporated on the ZnO electrons transportlayer, to obtain the QD light-emitting diode.

EXAMPLE 3

1) Prepare a mixture of the CuSCN and the QDs: dissolve 0.1 mg CuSCNpowder and 15 mg CdSe@CdS@ZnS QDs in 1 mL n-octane, mix well and form auniform mixture.

2). A plurality of preparation steps of the QLED device is as follows:spin coat a layer of the PEDOT:PSS holes injection layer on the ITOsubstrate; spin coat a layer of the TFB holes transport layer on thePEDOT:PSS holes injection layer;

3). Spin-coat the mixture of the CuSCN nanoparticles and the QDs on theTFB holes transport layer, and form a QD light-emitting layer containingthe CuSCN nanoparticles;

4). Followed by spin-coating a layer of the ZnO electrons transportlayer on the QD light-emitting layer;

5). Finally, an Al cathode is evaporated on the ZnO electrons transportlayer, to obtain the QD light-emitting diode.

EXAMPLE 4

1) Prepare a mixture of the CuSCN and the QDs: dissolve 0.05 mg CuSCNpowder and 20 mg CdSe@CdS@ZnS QDs in 1 mL n-octane, mix well and form auniform mixture.

2). A plurality of preparation steps of the QLED device is as follows:spin coat a layer of the PEDOT:PSS holes injection layer on the ITOsubstrate; spin coat a layer of the poly-TPD holes transport layer onthe PEDOT:PSS holes injection layer;

3). Spin-coat the mixture of the CuSCN nanoparticles and the QDs on thepoly-TPD holes transport layer, and form a QD light-emitting layercontaining the CuSCN nanoparticles;

4). Followed by spin-coating a layer of the ZnO electrons transportlayer on the QD light-emitting layer;

5). Finally, an Al cathode is evaporated on the ZnO electrons transportlayer, to obtain the QD light-emitting diode.

All above, the present disclosure provides a QD light-emitting diode anda preparation method therefor, and a light-emitting module and a displayapparatus. The present disclosure blends the QDs and the CuSCNnanoparticles into a membrane to prepare the QD light-emitting layer,and passivates a hole trap state on a surface of the QDs, as well asimproving a transport effect of the holes, making an injection of theholes and the electrons in the QLED achieve a balance, thus improving alight-emitting efficiency and a stability of the QLED.

It should be understood that, the application of the present disclosureis not limited to the above examples listed. Ordinary technicalpersonnel in this field can improve or change the applications accordingto the above descriptions, all of these improvements and transformsshould belong to the scope of protection in the appended claims of thepresent disclosure.

What is claimed is:
 1. A quantum dot (QD) light-emitting diode, wherein comprising an anode, a cathode, and a QD light emitting layer arranged between the anode and the cathode; wherein a material of the QD light-emitting layer comprises a plurality of QDs and a plurality of cuprous thiocyanate (CuSCN) nanoparticles, and a mass ratio between the QDs and the CuSCN nanoparticles is in a range of 0.001˜20:1.
 2. The QD light-emitting diode according to claim 1, wherein further comprising a holes injection layer arranged between the anode and the QD light emitting layer, a holes transport layer arranged between the holes injection layer and the QD light-emitting layer, and an electrons transport layer arranged between the cathode and the QD light-emitting layer, the holes transport layer overlays the QD light-emitting layer.
 3. The QD light-emitting diode according to claim 1, wherein a thickness of the QD light-emitting layer is 10˜100 nm.
 4. The QD light-emitting diode according to claim 1, wherein a size range of the CuSCN nanoparticles is 0.5˜50 nm.
 5. A display apparatus, wherein comprising the QD light-emitting diode according to claim
 1. 